Stencil paper and coating composition



United States Patent Ofifice 3,062,675 Patented Nov. 6, 1962 3,062,675 STENCIL PAPER AND (IQATDIG COMPQSITION Loren E. Shelfio, Palatine, iii, assiguor to Weber Addressing Machine Co., Inc., Mount Prospect, 111., a corporation of Illinois No Drawing. Fiied Mar. 30, 1959, Ser. No. 802,617 10 Ciaims. (Cl. 117-355) The present invention relates to new and improved coating compositions for application to stencil paper for use in mimeographing. More specifically, the invention is directed to new and improved hot melt coating compositions for stencil paper, the improved stencil paper having these compositions applied thereto, and the methd of forming the compositions and applying them to the stencil paper base material.

Mimeograph stencils at the present time are prepared by applying a solvent solution coating to thin tissue-like paper with the coating being dried on the paper as a result of solvent vaporization. The tissue-like paper base commonly used has a weight of about 6 to 7 lbs. per 3000 sq. ft. and has a solvent solution coating applied thereto which is formed from nitro-cellulose combined with suitable plasticizers and solvents. This type of coating is applied by known methods with the plasticized nitro-cellulose being solvated in the presence of low boiling ethers, ketones, alcohols, etc. or combinations of various suitable solvents. The time required for volatilization of the solvents from the applied coating materially increases the total production time necessary to form the finished stencil paper product. The necessity of solvent removal and the low flash points of such solvents make the stencil paper coating operation hazardous and expensive. Additional equipment is required to provide adequate fire prevention as well as solvent recovery. Thus, it has been found and is generally recognized that solution coating of stencil paper of the type described has the following disadvantages and limitations:

(1) Production is slow and costly.

(2) A substantial fire hazard is involved and rather extensive preventive protection of a cost-increasing nature must be supplied.

(3) The use of solvents which are not retained in the final product and which must be recovered to maintain production cost at a minimum adds materially to the overall cost.

(4) Solution coating application is difficult to control with respect to coating weights applied to the paper base as well as other factors which affect the quality of the finished product.

In efforts to overcome the aforementioned problems and limitations, stencil paper manufacturers have attempted to formulate usable and acceptable hot melt coating compositions. Such compositions eliminate the necessity of solvent utilization and the several problems arising from such use. By way of example, upon the determination of a suitable hot melt coating composition, a stencil paper manufacturer can materially reduce his equipment requirements, time of completion of the coating process, factory fire hazard problems, and overall costs. Hot melt compositions proposed have included the use of waxes, resins and gums as film formers with these materials being plasticized with suitable oils and the like. These compositions have not been found to be generally acceptable as they fall short of the desirable properties of conventional solvent coatings of nitro-cellulose. The following disadvantages on a comparative basis are illustrative of the reasons why known hot melt coating compositions have not been successfully used in the industry to any great extent: I

(1) The flexibility of applied hot melt coatings of known type falls substantially below that of conventionalsolvent applied coatings.

(2) Hot melt coatings proposed to date have exhibited rather high viscosities making the same difficult to apply to the stencil paper base material.

(3) Hot melt coatings have been found to dissolve and become weakened in the presence of oil base inks.

(4) Storage stability of known hot melt coatings is poorer than that of solvent applied coatings.

It is an object of the present invention to provide-a new and improved hot melt coating composition for use in the manufacture of stencil paper for mimeographing, these compositions being readily and uniformly applied, resistant to standard inks, of adequate flexibility, and. of adequate stability.

A further object is to provide a new and improved mimeograph stencil paper having applied thereto the coating composition of the present invention.

Still a further object is to provide a new and improved method of forming a hot melt stencil paper coating composition and applying the same to the stencil base paper.

Other objects not detailed specifically set forth will become apparent from the following detailed description of the invention.

The following symbolic diagram illustrates the invention:

Stencil Paper Base It has been found that an improved hot melt stencil paper coating composition can be formed by combining ethyl cellulose with high melting" and boilingplasticizers which are compatible therewith, the composition 'then being essentially completed by the addition of a light weight mineral oil. The ethyl cellulose may have an ethoxyl value in the range of 44.5% to 49.5% and a viscosity of 7 to 50 centipoises when measured in a 5% solution of a mixture of parts toluene and 20 parts ethanOl. Ethyl celluloses having an ethoxyl value between 47.5% to 49% and a viscosity between 15 to 25 centipoises are preferred. The high melting plasticizer constituent is preferably a suitable aliphatic amidesuch as hydrogenated tallow acid amide which i'savailable under the trade designation of Armid H.T. (Armour &;Company, Chicago, Illinois). Other general classes; of suitable high melting plasticizers include vegetable'waxes and fatty acids. The high boiling plasticizer constituent may be any suitable high boiling ester, vegetable oil or fatty acid, and in the preferred formulation specified below, this constituent is butyl oleate. The light weight mineral oil preferred is Saybolt second paraflin'mineral oil although any suitable light weight mineral oil may be used.

The following example illustrates a preferred coating composition formulation of the present invention.

Example I In preparing the coating composition set forth in the foregoing example, the color pigments are milled into five times their weight of mineral oil to form a uniform pigment-oil dispersion. This dispersion is then combined with the remaining constituents under thorough mixing and melting together at a temperature within the range of about 270 to 340 F. The resulting hot melt composition is then applied as a coating to any suitable stencil base paper utilizing known hot melt coating procedures and equipment. During coating application, it is pre ferred that the composition be maintained at a temperature of about 300 F. for efiicient application thereof. The composition will also be preferably applied on the stencil paper base in amounts ranging from about 15 to 25 lbs. per 3000 sq. ft. of paper base. The composition designated exhibits a sufiiciently low viscosity to be easily applied as a coating and, upon extended periods of storage, there has been no evidence of deterioration even under temperature conditions extending up to 360 F.

As a result of the utilization of the coating composition of the present invention, the following important characteristics have been present in the stencil paper:

(1) The paper exhibits improved sensitivity to typing and handwriting as comppared with solvent solution coated stencil paper.

(2) While the flexibility of the stencil paper coated with the composition of the present invention is not quite equal to the flexibility of solvent solution coated stencil paper, the flexibility obtained is nevertheless entirely satisfactory.

(3) There is no deterioration of the coating on the paper as a result of application thereto of oil, water, glycerine or glycol base mimeograph inks.

(4) The hot melt coated stencil paper of the present invention provides for a sharper copy for mimeographing purposes than known solvent solution coated stencil paper.

The following examples further illustrate certain variations in the constituents used in forming a suitable coating composition coming within the scope of the present invention.

Example II Constituents: Percent by weight Ethyl cellulose 1O Dibutyl v phthalate 30 Armid HT 15 Light Weight paraffin oil 44 Color pigments 1 100 p Example III Constituents: I Percent by weight Ethyl cellulose 30 Tricresyl phosphate 40 Stearic acid 19 Light weight paraffin oil -cz Color pigments 1 100 Example IV Constituents: I Percent by weight Ethyl cellulose 10 Castor oil 10 Diglycol stearate z 10 Light weight parafiin oil 70 100 Example V Constituents: Percent by weight Ethyl cellulose 24 Ar'mid HT 5 Butyl ole-ate 40. Light weight paraffin oil 30 'Color pigments 1 The ethyl cellulose used in the various examples is available on the market under the identification of Type N-22 from Hercules Powder Company of Wilmington,

Delaware, and had an ethoxyl value of 47.5% to 49% and a viscosity of 22 centipoises. The following constituents may also be used in the coating composition of the present invention as high melting plasticizers.

Vegetable waxes: Fatty acids:

Candelillea Oleic acid Carnauba Stearic acid Castor wax In addition to the waxes and acids specified, diglycol stearate and montan wax may also be used.

Suitable specific high boiling plasticizers of the type specified above include the following:

The color pigments are preferably the iron blue pigments or the Chrome yellows, but any suitable dye or pigment may be used. Preferably, antioxidants and acid acceptors should be incorporated in the compositions. Preferred materials of this type are diamyl-phenol 2,6- ditertiarybutyl-para-cresol and octylphenol. Such materials will preferably be added in quantities maintaining the concentrations thereof in the compositions at less than 2%. These materials function to prevent oxidation and deterioration of the coatings.

The formulations specified may be varied over relatively Wide ranges. The ethyl cellulose constituent should be present on a weight basis from about 10% to 30%. The high melting plasticizer constituent can be varied on a weight basis from about 5% to 30%. The high boiling plasticizer constituent may be varied from about 10% to 50% by weight. The mineral oil content is preferably maintained between about 10% to 70% by weight.

Obviously certain modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A hot melt coating composition for stencil base paper application, said composition by weight consisting essentially of from about 10% to 30% ethyl cellulose combined with from about 5% to 30% high melting fatty amides and from about 10% to 50% high boiling esters which are compatible therewith as plasticizers, and further including from about 10% to 70% of a light weight mineral oil.

2. A hot melt coating composition for stencil base paper application, said composition by weight consisting essentially of from about 10% to 30% ethyl cellulose combined with from about 5% to 30% high melting fatty amides and from about 10% to 50% high boiling vegetable oils which are compatible therewith as plasticizers, and further including from about 10% to 70% of a light weight mineral oil.

3. A hot melt coating composition for stencil base paper application, said composition by weight consisting essentially of from about 10% to 30% ethyl cellulose, 5% to 30% hydrogenated tallow acid amide, 10% to 50% butyl oleate, and 10% to 70% light weight paraffin oil.

4. The coating composition of claim 3 wherein said ethyl cellulose has an ethoxyl value of from about 47.5% to 49.0% and a viscosity of from about 15 to 25 centipoises when measured in a 5% solution of a mixture of parts toluene and 20 parts ethanol.

5. A hot melt coating composition for stencil base paper application, said composition by weight consisting essentially of from about 10% to 30% ethyl cellulose, to 50% hydrogenated tallow acid amide, to 50% butyl oleate, 10% to 70% light weight parafiin oil, and less than 2% antioxidants and acid acceptors.

6. A hot melt coating composition for stencil base paper application, said composition by weight consisting essentially of about 20% ethyl cellulose, 10% hydrogenated tallow acid amide, 20% butyl oleate, 49% light weight paraflin oil, and 1% color pigments.

7. The coating composition of claim 6 wherein said ethyl cellulose has an ethoxyl value of from about 47.5% to 49.0% and a viscosity of from about to 25 centipoises when measured in a 5% solution of a mixture of 80 parts toluene and parts ethanol.

8. A hot melt coating composition for stencil base paper application, said composition consisting essentially of ethyl cellulose combined with a fatty amide plasticizer and a high boiling plasticizer selected from the group consisting of high boiling esters and high boiling vegetable oils, and further including a light weight mineral oil.

9. Stencil paper for use in mimeographing, said paper having a coating thereon in amounts of from about 15 to 6 25 lbs. per 3000 sq. ft. of paper, said coating being stable up to around 350 F. and being formed from about 20% ethyl celulose, 10% hydrogenated tallow acid amide, 20% butyl oleate, 49% light weight paraffin oil, and 1% color pigments.

10. Stencil paper for use in mimeographing, said paper having a coating thereon in amounts of from about 15 to 25 lbs. per 3,000 sq. ft. of paper, said coating being stable up to around 350 F. and consisting essentially of ethyl cellulose combined with a fatty amide plasticizer and a high boiling plasticizer selected from the group consisting of high boiling esters and high boiling vegetable oils, and further including a light weight mineral oil.

References Cited in the file of this patent UNITED STATES PATENTS 1,594,769 Davis Aug. 3, 1926 1,655,249 Smith Ian. 3, 1928 1,771,165 Davis July 22, 1930 2,271,724 Traylor Feb. 3, 1942 2,453,214 Figdor Nov. 9, 1948 2,500,617 Meigs Mar. 14, 1950 2,579,755 Pyle et al Dec. 25, 1951 2,995,468 Steiger Aug. 8, 1961 

1. A HOT MELT COATING COMPOSITION FOR STENCIL BASE PAPER APPLICATION, SAID COMPOSITION BY WEIGHT CONSISTING ESSENTIALLY OF FROM ABOUT 10% TO 30% ETHYL CELLULOSE COMBINED WITH FROM ABOUT 5% TO 30% HIGH MELTING FATTY AMIDES AND FROM ABOUT 10% TO 50% HIGH BOILING ESTERS WHICH ARE COMPATIBLE THEREWITH AS PLASTICIZERS, AND FURTHER INCLUDING FROM ABOUT 10% TO 70% OF A LIGHT WEIGHT MINERAL OIL. 